Rotary compressors generally are capable of reverse operation wherein they act as expanders. Reverse operation can occur at shutdown when the closed system seeks to equalize pressure via the compressor thereby causing the compressor to run as an expander with negligible load. This problem has been addressed by providing a discharge check valve, as exemplified by commonly assigned U.S. Pat. Nos. 4,904,165 and 5,088,905, located as close to possible to the scroll discharge to minimize the amount of high pressure gas available to power reverse operation. As long as any high pressure gas is available to power reverse operation, some movement of the orbiting scroll will take place with attendant noise even if there is no attendant danger to the scroll compressor. Even if not harmful, the noise can be annoying and its reduction and/or elimination is desirable. This was addressed in commonly assigned U.S. Pat. No. 5,167,491 where the compressor is unloaded prior to shutdown. The real problem is due to the lack of a load in reverse operation at shutdown. Without a load in reverse operation, the compressor components may be damaged due to excessive speed/stress.
Under conditions that normally result in reverse flow through the compressor such as very low speed operation, a power interruption or shutdown, a continuous, unimpeded flow path is established through the wraps. The unimpeded flow path permits pressure equalization through the compressor while preventing high speed reverse operation of the pump unit. Also, the present invention prevents powered reverse operation of single phase compressors where power is restored during reverse operation.
It is an object of this invention to prevent powered reverse operation in a scroll compressor.
It is another object of this invention to prevent the noise associated with reverse rotation of the scrolls of a scroll compressor.
It is a further object of this invention to lower the starting torque as a result of reduced scroll eccentricity at startup. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.
Basically, under conditions subject to producing reverse operation, the scroll wraps are separated so as to provide a continuous, unimpeded path through the scrolls.